Method for the liquefaction and separation of gases with the aid of external work



Feb. 23. 1926.

A. SELIGMANN METHOD FOR THE LIQUEFACTION AND SEPARATION OF GASES WITH THE AID OF EXTERNAL WORK Filed Feb. 21, 1924 300 gso 260 Patented Feb; 23, 1926.

UNITED STATES PATENT OFFICE.

ARTHUR SELIGMANN, OF BREMEN, GERMANY.

METHOD FOR THE LIQUEFACTION AND SEPARATION OF GASES WITH THE AID OF I EXTERNAL WORK. Y

Application filed February 21, 1924. Serial No. 694,273.

To all whom. it may concern:

Be it known that I, ARTHUR SnLIGMANN, a citizen of the Germany, residing at Bremen, Germany, have invented certain new and useful Improvements in aMethod for the Liquefaction and Separation of Gases with the 'Aid of External Work (for which I have filed application in Germany May 26, 1922); and I do hereby declare the following to be a full, clear,.and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same. My invention relates to an improved method for the liquefaction and separation of gases with the aid of external work. It would be theoretically ossible per S6 to completely liquefy lique able gases merely by expansion in doing outer work. Only in this manner the minimum of energyconsumption can be realized. Practically it is however impossible to work a power engine perfectly, for instance at the temperature of the liquid air being under atmospheric pressure (80 abs.).. The first technical air liquefaction (Linde) was carried through in abandoning the outer work, merely with the aid of the internal work by throttling or by a method which is extremely unfavorable from a heat-theoretical point of view. Subsequently experiments have been made to use expansion machines again for dimin ishing the energy consumption. The methods which has been mainly applied in practice, that by Claude and that by Heylandt, must be satisfied with producing only a part of the refrigerating duty by outer work, for the remainder the throttling must be used. According to both these methods one proceeds in such a manner that the air isdivided and only the one part-current is sent through the power engines.

According to my improved method only a part of the refrigerating duty takes place in'an expansion machine and the method differs from the known methods essentially in that the decrease of pressure but not the quantity of the gas are divided.

e accompanying drawing illustrates the idea of the invention.

Fig. 1 is a diagram and Fig. 2 illustrates the process in a diagram which has coordinates as the specific heat contents 2' and the logarithm of the pressure log. 72, which is especially adapted for the comparison of methods of this kind. The numerals relate.

to air. The curves drawn in full lines are isotherms for the inscribed absolute temperatures, the horizontal curves drawn in dash lines are throttle curves and their distances from each other correspond to. 20

ures by the same numerals. Although as examp e an air liquefying process with double circuit has been chosen, my invention is not limited to such aprocess. A simple circuit may also be used. The temperatures and pressures are indicated in absolute measure.

In the high pressure, compressor a the air is isothermically compressed at 290.ab's. from 20-200 atm.- abs., forced through the first part of the counter current apparatus 12, in being cooled isobarically to 238, then adiabatically expanded to 142 atm. in the expansion cylinder f, at which occasion it cools down to213 and produces a working efliciency-equal to 7 kcal/k The air is further isobarically cooled 1n thesecondpart of the counter" current apparatus 6 and throttled in the throttle valve 0 to 20 atm.

again by a, the liquid however is throttled a second time in the valve 0? to 1 atm. in cooling down tov 80 and in being evaporated again for 49%, The liquid which now remains is the desired final product. The cold vapour is conducted under equal pressure and heat absorption through I) and forced back isothermically from the low pressurecompressor e together with the required qpa'ntity of fresh air into the suction tube 0 a. t

' Owing to the fact that part of the refrigerating efliciency is produced by throttling at lowest temperature it is possible to make the other part work at considerably higher temperature, whereby the difficulties connected with the working of the power engine are considerably reduced. The adiabatic refrigerating duty could theoretically be placed at a higher or lower temperature than definite the state 4 at the admission into the I cylinder can evidently no longer be freely selected on the adiabate' but the required refrigerating duty is clearly determined owing to the heat transmission in the counter current apparatus. It seems unnecessary to discuss the manner of calculation. In practical application the temperature at the end of the expansion will be of such a low degree that the working and lubricating of'the machine can just /be effected without any difliculty.

Although it is theoretically better if a greater percentage of the total refrigerating duty is produced by performing outer work, so that in this respect the commonly used methods appear to be superior, it must not be overlooked that, according to my method the adiabatic expansion-which theoretically is considered to be right can be much better converted into practice than according to the commonly used methods. The insulating of the cylinder against access of heat from the outside is to be carried through in a much better manner as the cylinder does by far not get so cold as that of Heylandt or as that of Claude, and it is further of considerably smaller size, as its dimensions are evidently determined by the volume of the air at the end of the expansion, the air being, according to my method at this moment under higher pressure. In all piston machines the wall losses (which means the irreversible transmission of heat between the inflowing and outflowing gases) are especially disturbing, these losses are however directly proportional to the temperature difference which occurs in the .cylinder. This temperature difference is also considerably smaller than according to Claudes method and scarcely to be compared with the enor-' mous drop of temperature which characterizes the Heylandt method, In my method the losses due to clearance are further much smaller'as the pressure ratio is considerably smaller than according to the two methods pressure, this being somewhat diflicult but not im ossible.

In t 6 case that the liquefaction of the as is not the final ob Qct but only the means or separating it into its constituents, which in this case have to be delivered hot and at gaseous state, the method can be applied.

In the counter current apparatus quantitatively other conditions will then prevail but qualitatively the same conditions. The quantity of back-flowin gases is equal to the quantity of the a vancin gases but their specific heat is lower at t e expanded state. Consequently a part of the refrigera- 4 tion duty can be performed also in this case at moderate temperature.

What I claim is:

1. A method for liquefaction and separation of gases with the aid of external work performance in which the total quantity of gas circulating in the apparatus is at first preliminarily cooled in counter current, then partly expanded in a machine in performing work, cooled further in counter current and finally completely expanded by simple throttling.

2. A method for the liquefaction and separation of gaseous mixtures containing helium with the'aid of external work performance in which the total quantity of gas circulating in the aparatus is at first preliminarily cooled in counter current, then partly expanded in a machine in performing work, cooled further in counter current and finally completely expanded by simple throttling the state at the end of the last workperforming expansion being situated with in the integral inversion curve of the throttling action.

In testimony whereof, I aflix my signature.

ARTHUR SELIGMANN. 

